Particulate, absorbent, polymeric compositions are capable of absorbing large quantities of liquids such as water and body exudates and which are further capable of retaining such absorbed liquids under moderate pressures. These absorption characteristics of such polymeric compositions make them especially useful for incorporation into absorbent articles such as diapers. For example, U.S. Pat. No. 3,699,103 issued to Harper et al. on Jun. 13, 1972 and U.S. Pat. No. 3,670,731 issued to Harmon on Jun. 20, 1972, both disclose the use of particulate, absorbent, polymeric compositions (also referred to as hydrogels, superabsorbent, or hydrocolloid materials) in absorbent articles.
Conventional particulate, absorbent, polymeric compositions, however, have the limitation that the particles are not immobilized and are free to migrate during processing and/or use. Migration of the particles during processing can lead to material handling losses during manufacturing operations as well as nonhomogeneous incorporation of the particles into structures in which the particles are being used. A more significant problem, though, occurs when these particulate materials migrate during or after swelling. Such mobility leads to high resistance to liquid flow through the material due to the lack of stable interparticle capillary or liquid transport channels. This phenomenon is one form of what is commonly referred to as "gel blocking".
One attempt to overcome the performance limitations associated with particle mobility in the context of their use in absorbent articles has been to immobilize the particulate, absorbent, polymeric compositions by the addition of large quantities of liquid polyhydroxy compounds that act as an adhesive to hold the particles together or to a substrate. An example of this technology is disclosed in U.S. Pat. No. 4,410,571 issued to Korpman on Oct. 18, 1983. While this approach does limit migration before and, to some extent, during swelling, the particles eventually become detached from each other upon presentation of excess liquid to such polymeric compositions, resulting again in the breakdown of any preexisting capillary channels between the particles.
A more recent solution proposed to overcome the problem of absorbent particle mobility is to form these particles into aggregate macrostructures, typically as sheets of bonded absorbent particles. See U.S. Pat. No. 5,102,597 issued to Roe et al. on Apr. 7, 1992. These aggregate macrostructures are prepared by applying an interparticle crosslinking agent to absorbent polymeric precursor particles, physically associating the precursor particles, and reacting the interparticle crosslinking agent with the polymeric material to form interparticle crosslink bonds between the particles. Since under certain conditions the macrostructures can be somewhat inflexible and brittle, a plasticizer can be incorporated into the macrostructure. The plasticizer may be water, high molecular weight hydrophilic organic solvents, or polymeric solutions, or mixtures thereof. See Column 17, line 57 through Column 18, line 15 of Roe et al.
While the macrostructures of Roe et al. are useful in absorbent articles, the specific embodiments taught therein tend to be inflexible as made, or to lose flexibility upon exposure to conditions of high temperature and/or low humidity that may occur under normal storage conditions. For example, absorbent articles are commonly exposed to temperatures of over about 120.degree. F. and/or Relative Humidities of less than about 20% for extended periods in nonclimate controlled storage facilities, e.g., for several hours in car trunks or a month or more in a warehouse. As a result, the macrostructures tend to become brittle, crack or otherwise break apart, thereby diminishing the original advantage of immobilizing the absorbent material to improve absorption. The macrostructures also tend to become stiff, thereby decreasing the comfort of the wearer of the absorbent article.
Therefore, it is an object of the present invention to provide a flexible, porous, absorbent, polymeric macrostructure that retains sufficient flexibility under the conditions of high temperature and/or low humidity that may occur under normal storage conditions. It is a further object of the present invention to provide flexible, porous, absorbent polymeric macrostructures that remain intact and transport liquid even upon saturation with excess liquid, even after exposure to such conditions.
It is another object of the present invention to provide a method for producing such flexible, porous, absorbent polymeric macrostructures.
Another object of the present invention is to provide improved absorbent products, absorbent members, and absorbent articles (such as diapers or sanitary napkins) incorporating the flexible, porous, absorbent polymeric macrostructures of the present invention.